I know you cant get hp fire with 31 speed IVs, but you can have 30 and at level 50 it doesnt matter wether it is 31 or 30, it will be the same.
but if you say that perfect sp.def increase the chances of hp fire, then your doing everything right.
Id still like to have it. You should work with Power Items, cause they make sure that one specific stat is always given to the children.
I have a trade thread, pick something you need and then post it there, please.